Material and splint for orthopaedical, surgical and veterinary use and method of making same

ABSTRACT

A thermoplastic material, mainly to be used for splints and supports in orthopaedical, surgical and veterinary practice, is proposed for the fixation of body parts, the material including a copolymer of ε-caprolactone, polyurethane, and ethylene-butylene-styrene mixed with triallylcyanurate and oleic acid-imide, the copolymer mixture being gamma irradiated after processing, such that a degree of cross-linking of the molecules and a partially crystalline configuration results in a molded material with reproducible flexibility, elasticity and reciprocal stretch properties.

The present invention relates to a thermoplastic polymer material to beapplied for orthopaedical, surgical and veterinary use, shaped assplints, artificial parts, prothesis, bandages and dressings.

The material ought to be used in suitable shapes for said practices as asupporting gird or splint and it shall comply with special requirements,which are not claimed for other plastic articles.

Polymer plastic materials have been proposed already for similarpurposes, in order to forestall the disadvantages of gypsum splints.

In U.S. Pat. No. 3,692,023 polymers or mixtures of poly-ε-caprolactoneand polyvinylethylether are described, which can be put upon fabric orgauze. This material was to be wrapped, in a warmed condition, aroundbroken limbs, and after cooling down it formed a relatively hardsupporting means, which could be removed again manually by warming upsame.

In U.S. Pat. No. 4,175,177 orthopaedical bandages were described,consisting of copolymers of ε-caprolactone and acrylates.

Now more suitable materials have been sought in order to control theflexibility, bending strength, reciprocal elasticity and tensilestrength in a reproducible manner.

The materials, which are already known, have been studied and comparedwith each other.

From these investigations it became apparent, that the followingrequirements should be met merely in an accurate way:

1. Application of a thermoplastic polymer without any supportingmaterial.

2. The material must have the property to be deformed easily.

3. The material shall be fit for repeated use.

4. The material should have a high compression strength.

5. The material should have a defined elasticity.

6. The material should have a resistance to remaining elongation.

The phenomena of elasticity and resistance to elongation, as well as thecompression strength, depend from the degree of crystallinity, thecross-linking index and the shape of the molecular chains.

A suitable material for surgical and orthopaedical practice, consistingof a composite of layers of poly-ε-caprolactone and a polyester with anupper layer of polyurethane foam with open cells has been described inEuropean patent 0 263 552 of applicant.

A novel mixture of improved copolymers with a plasticizer has now beendeveloped.

Hereby use was made of insight and further reflections on the structureof materials obtained by fundamental research. The structure of thematerials is shown on page 5.

The process to obtain the present material according to the invention ischaracterized by a copolymerization by heating equimolecularweight-quantities of ε-caprolactone, polyurethane ofpolyoxypropylene-glycol and toluene-di-isocyanate withethylene-butylene-styrene-copolymer, while during the formation of thismixed copolymer triallyl-cyanurate in an amount of 0.3 to 3.5% wt./wt.,related to the total mass, and about 1% wt./wt. of oleic acid imide as aplasticizer are added, and the product, cast in shapes of block sectionsor sheeting is then irradiated by Gammaradiation up to 2.5 Megaradduring a short period.

By this method a material is obtained, which by its partialcross-linking of bundles of macromolecular chains with an isotacticstructure and its partial crystallinity of 5-10% can be processedsuccessfully in injection moulds with an inner coating ofpolytetrafluorethylene, to obtain desired shapes for practical surgeryand orthopaedy.

To a small part of the above raw materials during the last step somewater can be added, such that a soft foamed layer with open cells isformed, which at the elevated temperature is attaching to the surface ofthe shapes in a thickness of 0.5 to 1.0 mm.

The temperature of the copolymerization reaction is ranging from 45° to180° C., depending from the plasticizer contents.

The elasticity, crystallinity and stretch properties depend from theenthalpy of deformation. A measure for this quantity has been developedby Mooney and Rivlin, described in "Journal of Applied Physics", Vol.II, (1940), pages 582 a.f.

A review of the evaluation of similar materials is represented in"Elasticity and Structure of Polyurethane Networks", Dissertation of R.Blokland, Delft Technical University, 1968.

A stretched elastomeric copolymer of the type of the present materialhas properties in accordance with the formula of Mooney and Rivlin:

    F=(C.sub.1 +λ.sup.-1 ·C.sub.2)·(λ-λ.sup.-2),

Wherein the following parameters appear:

F=strain force [dyn/cm² ]

C₁ =constant for basic polymer [Kg/cm² ]

C₂ =Constant for copolymer [Kg/cm² ]

λ=Stretch.

The enthalpy of deformation of each component is:

    ΔG=1/2·C·(λ.sub.x.sup.l +λ.sub.y.sup.2 +λ.sub.z.sup.2 -3)

wherein the symbols are the following:

ΔG=Enthalpy of deformation,

C=Constant of the component material,

λ_(x) =Stretch in x-direction,

λ_(y) =Stretch in y-direction,

λ_(z) =Stretch in z-direction.

The elastic deformation is leading to an increase of the crystallinityand of the enthalpy of deformation (decrease of the entropy).

For the polyurethane-copolymers with ethylene-butylene-styrene andcaprolactone-components the values of the constants C at a standardtemperature of 25° C. are as follows:

Basic polymer: C₁ =3,30 Kg/cm²

Copolymer: C₂ =2,00 Kg/cm².

These values can be altered within ranges by the addition of thetriallylcyanurate and of the oleic acid-imide, such that a variety ofwell-defined properties can be obtained.

By the gamma-irradiation a reverse effect to some extent is obtained,such that every desired mechanical property with this versatile polymermaterial according to the invention can be reached, which is veryimportant for the medical treatment.

It is important that the shaped material in practice will remain at itsplace as required, that it will not slide or slip and that it will notdeform if no pressure is applied, and moreover that it will not stick atthe skin of the patient.

The material as developed according to the present invention has aso-called "plastic memory", resulting from its special molecular andcrystalline structure, as described, such that after adaptation in theadjusted shape as a splint or support, it will have some suppleness at aslightly elevated temperature and that it presses softly at the part ofthe body, the limb or the organism in question.

The product is not restricted in its application to orthopaedical orsurgical possibilities of use, but it might be used as well fortechnical purposes, such as the manufacture of filter aids, membranesand sieves, because it can be made porous and specifically permeable inthin layers. This renders the possibilty of use in specialized clinicaland analytical apparatus.

Furthermore the possibility of recycling of the present material isimportant, because it can be reduced into the form of particles and itcan be granulated and reshaped anew by extrusion and for injectionmoulding.

The present invention relates to the preparation, processing andapplications of the described material.

For special paramedical applications, such as arch supports and suchlikeor similar expedients, the polymer foam layer on the surface of thearticles can be replaced partly or entirely by a surface treatment witha suspension of a neutral scourer, such as e.g. pumice powder.

The chemical structures of the organic building parts of the copolymermixture are rendered in the enclosed formula sheet with formulae 1 to 5.The copolymer mixture is innocuous for human and animal tissue.

As polycaprolactone is an aerobic-biodegradable material, thecompositions according to the present invention are explicitlycompatible with the environment. ##STR1##

I claim:
 1. A method for the production of a deformable material fororthopaedical, surgical, veterinary and technical applications, basedupon poly-ε-caprolactone, wherein equimolecular weight amounts ofε-caprolactone, polyurethane prepared of polyoxypropylene glycol andtoluene-di-isocyanate, and ethylene-butylene-styrene-copolymer arereacted together under heating, and with reflux cooling of vapoursduring said reaction, triallylcyanurate in an amount of 0.3 to 3.5%wt./wt. and slowly oleic acid-imide in an amount of about 1% wt./wt. ofthe total mass are added, and the reaction product is cooled down,washed and granulated, and brought into the desired surgical ortechnical shape by injection moulding or extrusion, followed byirradiation with gamma rays of up to 2.5 Mrad, to obtain a solidflexible shape of flexibility and elasticity, as required for practicaluse.
 2. A method for the manufacture of orthopaedical and surgicalsplint--or supporting means consisting of thermoplastic polymermaterial, wherein a shaped product obtained according to claim 1 iscoated with a thin layer of a scourer.
 3. A method for the manufactureof articles according to claim 2, wherein a thin layer of weak open-cellfoam of polymer is spread upon the surface of the scourer. 4.Orthopaedical and surgical supporting means for the fixation of bodyparts after a fracture or an operation, wherein said means consistentirely of a material manufactured according to claim 2, or comprisepartly such a material.
 5. Orthopaedical and surgical supporting meansfor the fixation of body parts after a fracture or an operation, whereinsaid means consist entirely of a material manufactured according toclaim 3.